This invention is concerned with improvements in or relating to toe box and/or metatarsal protectors as used in safety footwear, namely boots and shoes that are worn in locations where there is danger of impact or compression forces being applied to and injuring the feet of the wearers.
Many industries now require that at all times workers wear safety footwear to protect their feet against injury caused, for example, by blows from falling objects, or crushing such as may be caused by a vehicle wheel rolling over the foot. Almost all safety footwear currently available comprise a toe protector, usually of steel, alternatively called a box toe or a toe box, providing a protective arch above the toes through which any compression or impact force applied to its top surface is transmitted to the insole on which it rests, and through the insole to the outsole and the ground. It is a requirement for official certification (more details of which are given below) that the toe box is incorporated into the footwear during its manufacture so as to be an integral part thereof. Also, provision is now commonly made to protect the metatarsus, namely the five long bones of the instep extending from the toes to the remainder of the bones of the foot. Many of the prior proposals for metatarsal protection comprise a guard that is applied to the exterior of the boot, but increasingly the protector is incorporated into the footwear as an integral part, it also being arranged so that forces applied to it are transmitted through the insole and outsole to the ground.
The Occupational Health and Safety Association (OHSA) specifies test and performance standards that have been established by American National Standards Inc. (ANSI) which safety footwear must pass if they are to be certified by them. The current standards are identified as ANSI 241/1999. The Canadian Standards Association (CSA) have adopted equivalent standards. In commercial practice these standards are sufficiently important that a safety boot is virtually unsalable unless it is entitled to and carries at least the minimum standard designation, i.e. I30 for toe impact force. Preferably, it is also certified as to its resistance to compression, the minimum designation being C30 for toe compression force, although for many jurisdictions and industries such certification is not a requirement. If a metatarsal protector is included then preferably it will at least meet the minimum standard of Mt30 for metatarsal impact force. The maximum standards available using the ANSI system are designated C75 and I75, with or without Mt75; there are also intermediate standards C50 and I50, with or without Mt50. The tests required and the standards indicated by these designations are explained below.
In the compression force test procedure for the toe box protector (there is no equivalent test procedure for a metatarsal protector) it is subjected to a crushing force using any standard compression testing apparatus that is applied at a rate of approximately 22.7 Kg per second (50 lbs; 222.4 Newtons) after an initial load of 227 Kg (500 lbs; 2224 Newtons) has first been applied. The vamp and upper of the test boot is cut away to allow insertion of a cylindrical steel test gauge into the toe box interior, the gauge being slid back and forth on the insole as the pressure is increased. The diameter of the gauge is 12.7 mm ({fraction (16/32)} in) for men""s footwear and 11.9 mm ({fraction (15/32)} in) for women""s footwear, and the compression resistance of the specimen is the compressive load that reduces the internal clearance in the toe box until movement of the gauge either forward or backward is first prevented. The three certifications available are designated C/30 or C/50 or C/75 and indicate respectively that the footwear will withstand a compression force of 455 Kg (1,000 lbs; 4,448 Newtons), or 795 Kg (1,750 lbs; 7,784 Newtons), or 1,134 Kg (2,500 lbs; 11,121 Newtons).
The test procedure for toe box impact force resistance involves dropping a standard weight of 22.7 Kg (50 pounds)with a cylindrical impact nose of 51mm (2 ins) length and 25.4 mm (1 in) diameter on to the toe portion of a specimen boot (size 9D for men""s footwear and 8B for women""s footwear) selected at random from stock after at least 14 days have elapsed from the time of completion of its manufacture. The impact occurs at a point at the approximate centre of the toe box and 13 mm (0.5 in)in front of its back edge, the weight being dropped from a height such that it exerts an impact force of the selected one of the three values, namely 40.7 Joules (30 foot pounds), or 67.8 Joules (50 foot pounds), or 101.7 Joules (75 foot pounds). The maximum downward compression suffered by the toe box during the impact, and the corresponding minimum internal clearance available to the wearer""s toes, is measured by a cylindrical lump of modelling clay or wax placed inside the box under the impact zone, the lump not exceeding 25.4 mm (1 in) in diameter and being shaped to extend between and make contact with the dome of the toe box and with the insole. After impact the cylinder is removed and its height measured at its lowest point to the nearest 0.794 mm ({fraction (1/32)} in). The required minimum internal clearance in the toe box interior during and after impact, as indicated by measurement of the compressed lump, is 12.7 mm ({fraction (16/32)} in) for men""s footwear and 11.9 mm ({fraction (15/32)} in) for women""s footwear. The footwear is certified according to the standard reached, and can be labelled with the designation I/30, I/50 or I/75 respectively.
The equivalent impact force test for a metatarsal protector employs similar equipment to that used to test the toe box, with the difference that the impactor at the bottom of the weight is a cylindrical bar extending transversely of the length of the boot. The test again requires an impact force of specified value, and this force is applied at a point 8.9 cm (3.5 in) from the outside tip of the 9D boot toe and 8.6 cm (3.375 in) for the 8B boot. A wax body of specified shape and composition is held in place within the boot beneath the impact zone, the required minimum internal clearance beneath the protector after the impact, as indicated by the height of the deformed body being 2.5 cm ({fraction (32/32)} in) for the male 9D boot and 2.4 cm ({fraction (30/16)} in) for the female 8B boot. The impact forces employed are again of nominal value 30 foot pounds (40.7 Joules), or 50 foot pounds (67.8 Joules), or 75 foot pounds (101.7 Joules), footwear that passes the respective test being certified with the designation Mt/30, Mt/50 or Mt/75 respectively.
Box toes of plastics materials are available, but they are significantly thicker than the commonly used steel box toe, so that it is more difficult to incorporate them into the boot construction without the resultant boot toe appearing much more bulky, especially in side elevation. Moreover, most safety footwear is manufactured by molding the outsole to the remainder of the boot and a box toe that is significantly thicker makes it impossible to use existing molds used with steel box toes, so that expensive new molds are required for each size of boot. Metatarsal protectors of plastics material, e.g. high density polyethylene or polypropylene (HDPE or HDPP), ABS and various proprietary nylons, are also available and again, if the above described impact standards are to be met the protector is such thickness that, even if the more expensive high modulus plastics materials are used, it is difficult to incorporate in safety footwear of standard sizes. The manufacture of both box toes and metatarsal protectors from plastics material has the advantage that even if of complex shape they can be molded in a single relatively inexpensive operation. There is also the possibility that protectors that are lighter in weight can also be produced. Manufacturers of safety footwear face an inherent marketing problem that whether the footwear is supplied by the employer at cost, or with a subsidy, or whether it is purchased directly by the wearer, it is basically a product for which a relatively low purchase price is required by the customer, so that minimization of manufacturing cost is of primary importance.
A problem which many combined toe and metatarsal protectors are intended to at least alleviate, and if possible overcome, is that structures which are strong enough to provide the necessary protection are also usually very stiff, to the extent that they make walking or kneeling difficult. German Laid-Open application (Offenlegungschrift) No. 2536443, published Feb. 17 1977, describes a combined toe and metatarsal protector for safety footwear which attempts to provide a solution to this problem. To this end the toe box and a metatarsal plate, which preferably are of steel but which can also be of molded plastics material or hardened light metal (sic), are separate from one another and the lower end of the metatarsal plate protrudes into a second cavity above the toe-receiving cavity provided by the toe box. This second cavity is of sufficient size to allow the required forward and backward flexing between the two parts, while restraining the metatarsal plate against unwanted displacement. There is no disclosure or teaching that the structure envisaged could be designed so as to improve the resistance of the resulting toe box to impact and compression forces.
It is therefore the principal object of the invention to provide a toe box protector, or a metatarsal protector, or a combination toe box and metatarsal protector, that can readily be molded from plastics material and meet at least the minimum test requirements for ANSI certification as described above, and preferably able to meet the maximum requirements.
It is another object to provide a toe box protector, or a metatarsal protector, or a combination toe box and metatarsal protector, molded from plastics material that is able meet the ANSI test requirements for certification as described above while being sufficiently lower in height in side profile that it can be incorporated by molding in safety footwear using molds previously employed for steel box toes.
In accordance with the present invention there is provided a toe box protector for safety footwear that comprise an upper and a sole joined to one another, the upper and sole each having respective outer and inner surfaces and having respective registering toe regions;
wherein the toe box protector comprises a body molded from plastics material to have a generally U-shaped transverse cross section, the body having a top portion constituting a base of the U and two side portions constituting respective sides of the U;
wherein the toe box protector when incorporated into safety footwear is interposed between the upper and sole toe regions, and when so interposed has an outer surface convex toward the inner surface of the upper and an inner surface concave toward the inner surface of the sole;
wherein the toe box protector also comprises a force receiving part having respective upper and lower surfaces and overlying the central part of the top portion outer surface with its lower surface spaced from the central part, the force receiving part being of concave shape toward the central part so as to provide an arcuate space of predetermined height between the force receiving part lower surface and the top portion central part outer surface and to have two transversely spaced junctions with the remainder of the body;
whereby compression and impact forces applied to the force receiving part urge the force receiving part toward the central part of the top portion with corresponding reduction in the height of the arcuate space and conversion of such compression and impact forces to corresponding longitudinal forces distributed along the transversely spaced junctions; and
wherein the thicknesses of the two body side portions, of the body top portion, and of the force receiving part, together with the height of the arcuate space, are such that the protector maintains a minimum internal clearance in the foot receiving cavity of 12.7 mm ({fraction (16/32)} in) for men""s footwear and 11.9 mm ({fraction (15/32)} in) for women""s footwear when subjected to a compression force of at least 455 Kg (1,000 lbs; 4,448 Newtons) or to an impact force of at least 40.7 joules (30 foot pounds).
Also in accordance with the invention there is provided a metatarsal protector for safety footwear that comprise an upper and a sole joined to one another, the upper and sole each having respective outer and inner surfaces and having respective registering metatarsal regions;
wherein the metatarsal protector comprises a body molded from plastics material to have a generally U-shaped transverse cross section, the body having a top portion constituting a base of the U and two side portions constituting sides of the U, the protector thereby defining a foot receiving cavity whose height constitutes its internal clearance;
wherein the metatarsal protector when incorporated into safety footwear is interposed between the metatarsal regions, and when so interposed has an outer surface convex toward the inner surface of the upper and an inner surface concave toward the inner surface of the sole;
wherein the metatarsal protector also comprises a force receiving part having respective upper and lower surfaces and overlying the central part of the top portion outer surface with its lower surface spaced from the central part, the force receiving part being of concave shape toward the central part so as to provide an arcuate space of predetermined height shape between the force receiving part lower surface and the top portion central part outer surface and to have two transversely spaced junctions with the remainder of the body;
whereby compression and impact forces applied to the force receiving part urge the force receiving part toward the central part of the top portion with corresponding reduction in the height of the arcuate space and conversion of such compression and impact forces to corresponding longitudinal forces distributed along the transversely spaced junctions; and
wherein the thicknesses of the two body side portions, of the top portion, and of the force receiving part, together with the height of the arcuate space, are such that the protector maintains a minimum internal clearance of 25.4 mm ({fraction (32/32)} in) for men""s footwear and 24 mm ({fraction (30/32)} in) for women""s footwear when subjected to an impact force of at least 40.7 joules (30 foot pounds).
Further in accordance with the invention there is provided a toe box and metatarsal protector that is a combination of the toe box and metatarsal protectors of the invention.